1. Field of the Invention
This invention relates to nylon fibers having unusual and beneficial dyeing characteristics. More specifically, the invention relates to nylon fibers which resist staining by acid dyes at ambient temperatures and yet are capable of being dyed at elevated temperatures with acid dyes without losing their resistance to staining by acid dyes at ambient temperatures. Conventional nylon fibers can be permanently stained at room temperature by acid dye colorants commonly found in household items, such as beverages, foods, cosmetics, medicines, etc. The nylon fibers of the invention have the ability at room temperature to resist staining normally caused by these colorants and therefore are particularly suited for use in the construction of carpets.
The term fiber as used herein includes fibers of extreme or indefinite length (i.e. filaments) and fibers of short length (i.e. staple). The term yarn, as used herein, means a continuous strand of fibers.
The terms "stain" and "staining" as used herein with reference to nylon fibers means discoloration of such fibers caused by the chemical reaction thereof with a substance such as an acid dye.
2. Description of the Prior Art
Carpet made from nylon fibers is a popular floor covering for both residential and commercial applications. Such carpet is relatively inexpensive and offers a desirable combination of qualities, such as durability, aesthetics, comfort, safety, warmth and quietness. Also, it is available in a wide variety of attractive colors, patterns and textures. However, nylon fibers are severely and permanently stained by certain artificial and natural colorants present in common household items, such as Kool Aid.RTM. and other soft drink beverages, and thus carpet made from nylon fibers is vulnerable to the spilling of such items. The vast majority of these colorants are acid dyes, all of which have been approved by the Food, Drug and Cosmetic Commission for human consumption. One of the most commonly used acid dye colorants and one which most severely stains nylon at room temperature is FD&C Red Dye No. 40 (hereinafter referred to as "Red Dye No. 40"). Red Dye No. 40 (also known as C.T. Food Red 17) has the following structures. ##STR1##
Nylon carpet fibers are often coated with a fluorochemical either before or after the carpet is made for the purpose of improving the antisoiling characteristics of the carpet surface. The fluorochemical reduces the tendency of soil to adhere to the fiber thereby making the removal of soil from the carpet much easier than if the fluorochemical were omitted and, although this fluorochemical treatment also reduces fiber wettability, it offers very little protection to the carpet from spills containing acid dye colorants unless such colorants are immediately removed from the carpet within five to seven minutes. In contrast to substances such as lipstick, shoe polish and motor oil which are capable of being physically removed from nylon carpet by recognized cleaning procedures, acid dye colorants, such as Red Dye No. 40, penetrate and chemically react with nylon to form bonds which make complete removal of such colorants from the nylon fibers impossible; the fibers are actually dyed by these colorants within minutes and, therefore, permanently stained.
Surveys of the carpet replacement market show that more carpets are replaced due to staining than due to wear. Therefore, there is a need in the art to provide nylon carpet fibers from which a more stain-resistant carpet can be made.